In the following description, a device to device communication environment of the present invention is briefly explained.
A device to device communication (hereinafter abbreviated D2D) communication literally means a communication between one electronic device and another electronic device. In a broad sense, the D2D communication may mean a communication between electronic devices or a communication between a human-controllable device and a machine. Recently, the D2D communication may generally indicate a wireless communication performed between electronic devices without human involvement.
In the early 1990's, in which the concept of the D2D communication has been initially introduced, the D2D communication has been recognized as remote control or telematics or the like and derivative markets of the D2D communication were very limitative. Yet, the D2D communication has grown rapidly for past few years and has become the globally noteworthy markets. Specifically, the D2D communication has considerably influence on such field as POS (point of sales), fleet management, remote monitoring of machinery and equipment, and the like. D2D communication in the future will be further utilized for various usages in connection with a small-scale output communication solution such as conventional mobile communication, wireless high-speed internet, Wi-Fi, ZigBee and the like and may lay the foundation of expansion to B2C (business to consumer) markets instead of being confined to B2B (business to business) markets.
In the era of the D2D communication, every machine equipped with SIM (subscriber identity module) card enables data transmission and reception and is capable of remote management and control. For instance, as D2D communication technology is usable for numerous devices and equipment including vehicles, trucks, trains, containers, auto-vending machines, gas tanks and the like.
According to a related art, since a user equipment is generally managed in an individual unit, a communication between a base station and a user equipment is mainly performed by one-to-one communication scheme. If many D2D devices communicate with a base station using the one-to-one communication scheme, a network overload may occur due to signaling with the base station. As mentioned in the foregoing description, if the D2D communication is rapidly spread, overhead occurred by communication between D2D devices or communication between D2D devices and base station may cause a problem.
According to a related art, study on a method of performing a seamless communication in case of a poor D2D connection state and a method of performing a mode change (handover to a cellular network) while performing a direct communication between devices is not satisfactory.